1. Field of the Invention
The present invention is directed to a method for producing rare earth oxysulfide powder.
2. Description of the Prior Art
Rare earth oxysulfide powders can be utilized as luminescent material powder for the manufacture of X-ray screens.
It is possible to produce translucent ceramics from such powders by means of pressing, preferably hot-pressing, scintillator elements, in turn, can be produced from these translucent ceramics for the X-ray detectors in computed tomography (CT) devices.
It is known to produce gadolinium oxysulfide powder by reducing doped gadolinium sulfite (see German PS 42 24 931). This method is complicated and requires the utilization of toxic sulfur dioxide gas for acquiring gadolinium sulfite from gadolinium oxide. Moreover, excessive sulfur is released in the form of sulfur dioxide and sulfur given the reduction of the gadolinium sulfite to gadolinium oxysulfide; this requires a complicated exhaust gas cleaning or purification. Therefore, it this known technique for the production of rare earth oxysulfide powder is technically complex and expensive.
The same is true for the method known from "Patent Abstracts of Japan", C-262, Jan. 24, 1985, vol. 9/No. 17, (for Japanese Application 59-164631), wherein rare earth oxysulfide powder is produced by reducing rare earth oxysulfate, with the rare earth oxysulfate being acquired by dissolving a rare earth oxide in sulfuric acid or sulfate, and the corresponding rare earth hydroxide is formed by adding an alkaline substance. The rare earth oxysulfate is acquired from the rare earth hydroxide by heating in an oxidizing atmosphere.